Polycarbonate is a thermoplastic that has excellent mechanical properties such as impact resistance, heat resistance and transparency. Polycarbonate is widely used in many engineering applications. Polycarbonates may be prepared by several processes including a melt process in which a carbonic diester is polymerized in a multistage reactor in the presence of a dihydroxy compound to yield a molten polycarbonate. Polycarbonate can also be prepared in a melt process by reacting a dihydroxy compound and an activated diaryl carbonate. New methods and apparatus for making polycarbonate are continually needed.